Angiogenesis, the process of developing a hemovascular network, is essential for the growth of solid tumors and is a component of normal wound healing and growth processes. It has also been implicated in the pathophysiology of atherogenesis, arthritis, corneal neovascularization, and diabetic retinopathy. It is characterized by the directed growth of new capillaries toward a specific stimulus. This growth, mediated by the migration of endothelial cells, may proceed independently of endothelial cell mitosis.
The molecular messengers responsible for the process of angiogenesis have long been sought. For example, Greenblatt et al., J. Natl. Cancer Inst. 41:111-124, 1968, concluded that tumor-induced neovascularization is mediated by a diffusible substance. Subsequently, a variety of soluble mediators have been implicated in the induction of neovascularization. These include prostaglandins (Auerbach, in Lymphokines, Pick and Landy, eds., 69-88, Academic Press, New York, 1981), human urokinase (Berman et al., Invest. Opthalm. Vis. Sci. 22:191-199, 1982), copper (Raju et al., J. Natl. Cancer Inst. 69:1183-1188, 1982), and various “angiogenesis factors” (e.g., see U.S. Pat. No. 4,916,073).
Angiogenesis factors play an important role in wound healing (Rettura et al., FASEB Abstract #4309, 61st Annual Meeting, Chicago, 1977) and likely play a role in the development of malignancies (Klagsburn et al., Cancer Res. 36:110-114, 1976; and Brem et al., Science 195:880-881, 1977), hence it would clearly be advantageous to identify new angiogenic agents.
DNA is a complex macromolecule whose activities are influenced by its base composition and base modification, as well as helical orientation. Bacterial DNA, as well as certain synthetic oligodeoxynucleotides (ODNs) containing unmethylated CpG sequences can induce proliferation and immunoglobulin production by murine B cells. Unmethylated CpG dinucleotides are more frequent in the genomes of bacteria and viruses than vertebrates. Recent studies suggest that immune recognition of these motifs may contribute to the host's innate immune response. (Klinman et al, Proc. Natl. Acad. Sci. USA 93:2879, 1996;. Yi et al, J. Immun. 157:5394, 1996; Liang et al, J. Clin. Invest. II 9:89, 1996; Krieg et al., Nature 374:546, 1995).
In mice, CpG DNA induces proliferation in almost all (>95%) of B cells and increases immunoglobulin secretion. This B-cell activation by CpG DNA is T-cell independent and antigen non-specific. In addition to its direct effects on B cells, CpG DNA also directly activates monocytes, macrophages, and dendritic cells to secrete a variety of cytokines. These cytokines stimulate natural killer (NK) cells to secrete γ-interferon (IFN-γ) and have increased lytic activity. However, although some of the effects of oligodeoxynucleotides containing unmethylated CpGs are known, many effects have yet to be elucidated.